---
title: ApolloClient
description: ApolloClient API reference
order: 11
---

import { TypescriptApiBox } from 'gatsby-theme-apollo-docs';

The `ApolloClient` class encapsulates Apollo's core client-side API. It backs all available view-layer integrations (React, iOS, and so on).

## The `ApolloClient` constructor

<TypescriptApiBox name="ApolloClient.constructor" />

The constructor for `ApolloClient` accepts an `ApolloClientOptions` object that supports the required and optional fields listed below. These fields make it easy to customize how Apollo works based on your application's needs.

### Example constructor call

```js
import { ApolloClient, InMemoryCache, createHttpLink } from '@apollo/client';

// Instantiate required constructor fields
const cache = new InMemoryCache();
const link = createHttpLink({
  uri: 'http://localhost:4000/',
});

const client = new ApolloClient({
  // Provide required constructor fields
  cache: cache,
  link: link,

  // Provide some optional constructor fields
  name: 'react-web-client',
  version: '1.3',
  queryDeduplication: false,
  defaultOptions: {
    watchQuery: {
      fetchPolicy: 'cache-and-network',
    },
  },
});
```

### Required fields

| Name | Description |
| - | - |
| `uri` | A URI pointing to the backend GraphQL endpoint that Apollo Client will communicate with. **Note:** One of `uri` or `link` is required; if both are specified, `link` will take precedence. |
| `link` | You can provide an Apollo Link instance to serve as Apollo Client's network layer. For more information, see the [advanced HTTP networking](../../networking/advanced-http-networking/) section. **Note:** One of `uri` or `link` is required; if both are specified, `link` will take precedence. |
| `cache` | Apollo Client uses an Apollo Cache instance to handle its caching strategy. The recommended cache is `InMemoryCache` which is provided by the `@apollo/client` package. For more information, see [Configuring the cache](../../caching/cache-configuration/). |

### Optional fields

| Name | Description |
| - | - |
| `name` | A custom name (e.g., `iOS`) that identifies this particular client among your set of clients. Apollo Server uses this property as part of its [Client Awareness](https://www.apollographql.com/docs/apollo-server/v2/features/metrics#Client-Awareness) feature. |
| `version` | A custom version that identifies the current version of this particular client (e.g., `1.2`). Apollo Server uses this property as part of its [Client Awareness](https://www.apollographql.com/docs/apollo-server/v2/features/metrics#Client-Awareness) feature. <br/><br/> Note that this version string is **not** the version of Apollo Client that you are using, but rather any version string that helps you differentiate between versions of your client. |
| `ssrMode` | When using Apollo Client for [server-side rendering](../../performance/server-side-rendering/), set this to `true` so that React Apollo's `getDataFromTree` function can work effectively. |
| `ssrForceFetchDelay` | Provide this to specify a time interval (in milliseconds) before Apollo Client force-fetches queries after a server-side render. This value is `0` by default. |
| `connectToDevTools` | Set this to `true` to allow the [Apollo Client Devtools](../../development-testing/developer-tooling/#apollo-client-devtools) Chrome extension to connect to your application's Apollo Client in production. (This connection is allowed automatically in dev mode.) |
| `queryDeduplication` | Set this to `false` to force all created queries to be sent to the server, even if a query with completely identical parameters (query, variables, operationName) is already in flight. |
| `defaultOptions` | Provide this object to set application-wide default values for options you can provide to the `watchQuery`, `query`, and `mutate` functions. See below for an example object. |

### Example `defaultOptions` object

```js
const defaultOptions = {
  watchQuery: {
    fetchPolicy: 'cache-and-network',
    errorPolicy: 'ignore',
  },
  query: {
    fetchPolicy: 'network-only',
    errorPolicy: 'all',
  },
  mutate: {
    errorPolicy: 'all',
  },
};
```

You can override any default option you specify in this object by providing a
different value for the same option in individual function calls.

> **Note:** The `<Query />` React component uses Apollo Client's `watchQuery` function. To set `defaultOptions` when using the `<Query />` component, make sure to set them under the `defaultOptions.watchQuery` property.

## `ApolloClient` functions

<TypescriptApiBox name="ApolloClient.watchQuery" />
<TypescriptApiBox name="ApolloClient.query" />
<TypescriptApiBox name="ApolloClient.mutate" />
<TypescriptApiBox name="ApolloClient.subscribe" />
<TypescriptApiBox name="ApolloClient.readQuery" />
<TypescriptApiBox name="ApolloClient.readFragment" />
<TypescriptApiBox name="ApolloClient.writeQuery" />
<TypescriptApiBox name="ApolloClient.writeFragment" />
<TypescriptApiBox name="ApolloClient.resetStore" />
<TypescriptApiBox name="ApolloClient.onResetStore" />
<TypescriptApiBox name="ApolloClient.clearStore" />
<TypescriptApiBox name="ApolloClient.onClearStore" />
<TypescriptApiBox name="ApolloClient.stop" />
<TypescriptApiBox name="ApolloClient.reFetchObservableQueries" />

## Types

<TypescriptApiBox name="ApolloClientOptions" />
<TypescriptApiBox name="DefaultOptions" />
